1. Field of the Invention
This invention pertains generally to pipettes, and more specifically to a replaceable tip and piston assembly with unique means of attachment to the pipette.
2. Description of the Background Art
In the area of clinical and analytical chemistry research, pipettes are used for handling precise quantities of liquid. This is important in the area of deoxyribonucleic acid (DNA) research generally, and particularly that pertaining to polymerized chain reactions (PCR) which requires handling separate samples involving picograms of DNA. In order to avoid samples being tainted, instead of individual pipettes being used, disposable pipette tips have been developed which, when used with programmable pipettes, are capable of handling minute quantities of liquid. These pipette tips often include pistons which reduce the per unit volume of liquid that can be drawn into the pipette tip, and permit extraction of liquid with extreme precision. The manner of attachment of the piston to the pipette is important for maintaining repeatability in measurements, and facilitating easy attachment and removal of the pipette tip.
In order to meet the need of precise liquid handling, various pipettes and pipette tips have been developed. For example, U.S. Pat. No. 4,442,722 issued to Meyer on Apr. 17, 1984, discloses a dual stroke air displacement pipette, attached to which is a removable pipette tip. U.S. Pat. No. 3,786,683 issued to Berman et al. on Jan. 22, 1974, discloses a pistol grip style air displacement pipette having replaceable pipette tips. U.S. Pat. No. 4,616,514 issued to Magnussen, Jr. et al. on Oct. 14, 1986, discloses an air displacement pipette having resilient clips on the outside of the pipette body to retain a removable pipette tip, the clips being expandable with an overextension of the plunger to release the pipette tip. U.S. Pat. No. 4,707,337 issued to Jeffs et al. on Nov. 17, 1987, discloses an air displacement pipette having recessed and extruded rings which mate for attaching and sealing a removable pipette tip. U.S. Pat. No. 4,748,859 issued to Magnussen, Jr. et al. on Jun. 7, 1988, discloses an air displacement pipette which uses recessed and extruded rings to attach and seal a removable pipette tip. U.S. Pat. No. 4,187,724 issued to Citrin on Feb. 12, 1980, discloses an air displacement pipette using recessed and extruded rings to attach a removable pipette tip. U.S. Pat. No. 4,072,330 issued to Brysch on Feb. 7, 1978, discloses an air displacement pipette having a slip-on pipette tip which uses a flexible adaptor cone for frictional engagement. U.S. No. Pat. No. 4,863,695 issued to Fullemann on Sep. 5, 1989, discloses an air displacement pipette using sealing ribs to attach and seal a pipette tip. U.S. Pat. No. 4,961,350 issued to Tennstedt on Oct. 9, 1990, discloses an air displacement pipette which uses generic tapered surfaces for mating and sealing with a pipette tip. U.S. Pat. No. 4,023,716 issued to Shapiro on May 17, 1977, discloses a positive displacement pipette having a plunger which extends into a snap-on pipette tip which can be ejected by an overextension of the plunger. Most of these patents disclose variations of pipettes and pipette tips which have locking tapers or rings, and which are generally air displacement pipettes having air seals which are difficult to maintain. Others are higher precision positive displacement pipettes using a piston which is part of the pipette itself, and which can become contaminated from sample to sample.
In order to overcome the problems with maintaining air tight seals and to prevent against cross-contamination of samples, several positive displacement pipettes using replaceable pistons have been developed. For example, U.S. Pat. No. 4,084,730 issued to Franke et al. on Apr. 18, 1978, discloses attaching a removable pipette piston to a conical-shaped clamping ring, the clamping ring being made of a resilient material which is squeezed to clamp a piston which is inserted through the center of the clamping ring. U.S. Pat. No. 4,501,163 issued to MacDermott et al. on Feb. 26, 1985, discloses a pipette with a removable piston, the piston being attached to a plunger in the pipette body, and a snap-on tip. U.S. Pat. No. 4,362,063 issued to Marteau d'Autry on Dec. 7, 1982, discloses a piston attached to a plunger in a pipette which can be extended through a capillary tube. U.S. Pat. No. 4,362,064 issued to Marteau d'Autry on Dec. 7, 1982, discloses a pipette piston which moves through a pipette tip and which is attached to the pipette with a resilient gripping ring attached to a plunger in the pipette. The pipette tips disclosed in these patents, however, do not have integral pistons which can be automatically installed and ejected along with the pipette tip. Therefore, they are difficult to install and remove, and do not guard against contamination which can result from physical handling of the pipette tip and piston during installation and removal.
An example of a pipette tip with an integral piston, and which can be installed and removed automatically without physical handling, can be found in U.S. Pat. No. 4,474,071 issued to Marteau d'Autry on Oct. 2, 1984. That patent discloses a pipette tip with an integral piston for use with a pipette having a plunger with a collet or female receptacle to engage the end of the piston.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, applicant's claimed invention.